System for consolidating organic matrix composites using induction heating

ABSTRACT

An apparatus for forming and consolidating organic matrix composites. An organic matrix composite panel comprising laid-up prepegs is placed between sheets of a susceptor material that is susceptible to inductive heating to form a workpiece. The resulting workpiece is placed within upper and lower dies formed of a material that is not susceptible to inductive heating. An induction coil embedded within the dies is energized and inductively heats the susceptor sheets surrounding the panel. The sheets in turn conductively heat the organic matrix composite panel. A pressure zone between the workpiece and one of the dies is pressurized to form the workpiece to the contour of a forming surface on one of the dies. The pressure in the pressure zone is maintained on the workpiece until the organic matrix composite panel is fully consolidated and formed.

The present application is a divisional application based upon U.S.patent application Ser. No. 08/169,655, filed Dec. 16, 1993, which was acontinuation-in-part of U.S. patent application Ser. No. 07/777,739,filed Oct. 15, 1991, now U.S. Pat. No. 5,410,132, and of U.S. patentapplication Ser. No. 08/092,050, filed Jul. 15, 1993, now U.S. Pat. No.5,410,33, which in turn is a divisional of U.S. patent application Ser.No. 07/681,004, filed Apr. 5, 1991, now U.S. Pat. No. 5,229,562. Thebenefit of the filing dates of which are claimed under 35 U.S.C. § 120;these applications and patents are incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to the consolidation and forming oforganic matrix composites, more specifically, the present inventionrelates to methods and apparatus for inductively heating, forming andconsolidating resins to make organic matrix composites.

BACKGROUND OF THE INVENTION

Fiber-reinforced resin (i.e., organic matrix) composite materials havebecome widely used, have a high strength-to-weight or highstiffness-to-weight ratio, and desirable fatigue characteristics thatmake them increasingly popular in weight, strength or fatigue criticalapplications.

Prepregs consisting of continuous, woven, or chopped fibers embedded inan uncured matrix material are cut to the desired shape and then stackedin the desired configuration of the composite part. The prepreg may beplaced (laid-up) directly upon a tool or die having a forming surfacecontoured to the desired shape of the completed part or the prepreg maybe laid-up in a flat sheet and the sheet may be draped over a tool ordie to form to the contour of the tool.

After being laid-up, the prepreg is consolidated (i.e., cured) in aconventional vacuum bag process in an autoclave (i.e., a pressurizedoven). The pressure presses the individual layers of prepreg together atthe consolidation/curing temperatures that the matrix material flows toeliminate voids and cures, generally through polymerization.

In autoclave fabrication, the composite materials must be bagged, placedin the autoclave, and the entire heat mass of the composite material andtooling must be elevated to and held at the consolidation or curingtemperature until the part is formed and cured. The formed compositepart and tooling must then be cooled, removed from the autoclave, andunbagged. Finally, the composite part must be removed from the tooling.

To supply the required consolidation pressures, it is necessary to builda special pressure box within the autoclave or to pressurize the entireautoclave, thus increasing fabrication time and cost, especially for lowrate production runs.

Autoclave tools upon which composite materials are laid-up are typicallyformed of metal or a reinforced composite material to insure properdimensional tolerances and to withstand the high temperature andconsolidation forces used to form and cure composite materials. Thus,autoclave tools are generally heavy and have large heat masses. Theentire heat mass of the tool must be heated along with the compositematerial during curing and must be cooled prior to removing thecompleted composite part. The time required to heat and cool the heatmass of the tools adds substantially to the overall time necessary tofabricate a single composite part.

In composite parts requiring close tolerances on both the interior andexterior mold line of the part, matched autoclave tooling must be used.When matched tooling is used, autoclave consolidation pressure is usedto force the matched tooling together to consolidate the compositematerial and achieve proper part dimensions. Matched tooling is moreexpensive than open faced tooling and must be carefully designed toproduce good results, adding to part fabrication costs.

An alternative to fabricating composite parts in an autoclave is to usea hot press. In this method, the prepreg is laid-up, bagged (ifnecessary), and placed between matched metal tools that include formingsurfaces that define the internal and external mold lines of thecompleted part. The tools and composite material are placed within thepress and then heated. The press brings the tools together toconsolidate and form the composite material into the final shape.Fabricating composite parts in a hot press is also expensive due to thelarge capital expense and large amounts of energy required operate thepress and maintain the tools.

Generally, in hot press operations, to obtain close tolerances, themassive, matched tooling is formed from expensive metal alloys havinglow thermal expansion coefficients. The tooling is a substantial heatsink that takes a large amount of energy and time to heat to compositematerial consolidation temperatures. After consolidation, the toolingmust be cooled to a temperature at which it is safe to remove the formedcomposite part thus adding to the fabrication time.

Another contributor to the cost of fabricating composite parts is thetime and manpower necessary to lay up individual layers of prepreg toform a part. Often, the prepreg must be laid up over a tool havingfairly complex contours that require each layer of prepreg to bemanually placed and oriented. Composite fabrication costs could bereduced if a flat panel could be laid-up flat and then formed into theshape of the part.

One method used to reduce the costs of fabricating composite materialsis to lay up a flat panel and then place the flat panel between twometal sheets capable of superplastic deformation as described in U.S.Pat. No. 4,657,717. The flat composite panel and metal sheets are thensuperplastically deformed against a metal die having a surface contouredto the final shape of the part. Typically, the dies used in suchsuperplastic forming operations are formed of stainless steel or othermetal alloys capable of withstanding the harsh temperatures andpressures. Such dies have a large thermal mass that takes a significantamount of time and energy to heat up to superplastic formingtemperatures and to cool down thereafter.

Attempts have been made to reduce composite fabrication times byactively cooling the tools after forming the composite part. Theseattempts have shortened the time necessary to produce a composite part,however, the time and energy expended in tool heat up and cool downremains a large contributor to overall fabrication costs.

The present invention is a method and apparatus for consolidating andforming organic matrix composites that avoid some of theabove-identified disadvantages of the prior art.

SUMMARY OF THE INVENTION

The present invention is a method and apparatus for consolidation oforganic matrix composites using inductive heating. In the presentinvention, the dies or tooling for the organic matrix composite partsare made from a material that is not susceptible to inductive heating.Examples of usable tool materials are ceramics or resin composites. Thetooling is strengthened and reinforced with fiberglass rods or otherappropriate reinforcements to withstand the temperatures and pressuresused to form the composite materials. Such materials decrease the costof tool fabrication and also generally reduce the thermal mass andweight of the tooling. Since the tooling used in the present inventionis not susceptible to inductive heating, it is possible to use thetooling in combination with inductive heating elements to heat thecomposite material. The present invention allows the composite materialto be inductively heated without heating the tools significantly. Thus,the present invention can reduce the time and energy required tofabricate a composite part.

Graphite or boron reinforced organic matrix composites may besufficiently susceptible because of their reinforcing fibers that theycan be heated directly by induction. Most organic matrix compositesrequire a susceptor in or adjacent to the composite material to achievethe necessary heating. The susceptor is heated inductively and transfersits heat to the composite material.

The present invention reduces the time and energy required toconsolidate resin composite prepreg lay-ups for a composite. Becauseinduction focuses the heat on the workpiece rather than the tool, thereis less mass to heat or cool. Inexpensive composite or ceramic toolingcan also be used. The lower operating temperature of the tools decreasesproblems caused by different coefficients of thermal expansion betweenthe tools and the workpiece in prior art forming systems. The presentinvention also provides an improved method for fabricating compositeparts to close tolerances on both the internal and external mold line ofthe part.

In a method for consolidating/or and forming organic matrix compositematerials, an organic matrix composite panel is laid up and then placedadjacent a metal susceptor. The susceptor is inductively heated and thenheats the composite panel by thermal conduction. A consolidation andforming pressure is applied to consolidate and form the organic matrixcomposite panel at its curing temperature.

Generally, the composite panel is enclosed between two susceptor sheetsthat are sealed to form a pressure zone around the composite panel. Thispressure zone is evacuated in a manner analogous to convention vacuumbag processes for resin consolidation. The workpiece (the two susceptorsand composite panel) is placed in an inductive heating press on theforming surfaces of dies having the desired shape of the moldedcomposite part, and is pressed at elevated temperature and pressure(while maintaining the vacuum in the pressure zone) to consolidate thecomposite panel into its desired shape.

The workpiece may include three susceptors sealed around their peripheryto define two pressure zones. The first pressure zone surrounds thecomposite panel and is evacuated and maintained under vacuum. The secondpressure zone is pressurized to help form the composite panel.

One preferred apparatus for consolidating and forming the organic matrixcomposite panels uses ceramic or composite dies. An induction coil isembedded in the dies. When the coil is energized with a time varyingcurrent, induction heats the susceptors which in turn heats thecomposite panel by conduction. Pressure is applied to at least one sideof the composite panel to consolidate and form it when it reaches thedesired consolidation temperature.

It is preferred to use reinforced, cast phenolic or ceramic dies.Reinforcing rods are embedded within the dies to increase their strengthby compressing the dies. The phenolic or ceramic dies may be reinforcedwith chopped reinforcing fibers, with a mat or weave of continuousfibers or with other reinforcements. The die usually includes a cavityadapted to receive a tool insert. The tool insert may include a formingsurface that defines the shape of the molded composite part. In thisway, different parts can be made simply by changing the insert ratherthan needing to replace the entire die.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an apparatus for consolidating andforming organic matrix composite panels;

FIG. 2 is a schematic cross-sectional view of the apparatus of FIG. 1;

FIG. 3 is a perspective view illustrating the induction coil;

FIG. 4 is a cross-sectional view of a flexible coil connector;

FIG. 5 is a partially exploded, partially cut away view of a portion ofthe apparatus of FIG. 1;

FIG. 6A is an enlarged cross-sectional view of part of an organic matrixcomposite panel after it has been placed within the tooling but beforeconsolidation and forming has begun;

FIG. 6B is an enlarged cross-sectional view of part of an organic matrixcomposite panel after consolidation and forming has begun;

FIG. 6C is an enlarged cross-sectional view of part of an organic matrixcomposite panel after consolidation and forming has been completed;

FIG. 7 is a flow chart showing an embodiment of the method ofconsolidation and forming of the present invention;

FIG. 8 is a partial perspective view of an organic matrix composite partincluding a close tolerance attachment section; and

FIG. 9 is an enlarged cross-sectional view of tooling for forming aclose tolerance section in a part using matched tooling.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, the inductive heating and forming apparatus 10 includes toolsor dies 20 and 22 mounted within an upper 24 and a lower 26 strongback,respectively. The strongbacks are each threaded onto four threadedcolumn supports or jackscrews 28. The jackscrews can be turned using abellows or other actuation mechanisms to move the upper strongback orlower strongback up or down in relation to each other.

Each strongback 24 and 26 provides a rigid, flat backing surface for theupper and lower die 20 and 22 to prevent the dies from bending andcracking during repeated consolidation and forming operations.Preferably, the strongbacks should be capable of holding the dies to asurface tolerance of ±0.003 inches per square foot of the formingsurface in the toolbox. Such tolerances help to insure that proper parttolerances are achieved. The strongbacks may be formed of steel,aluminum, or any other material capable of handling the loads presentduring forming. However, materials that are nonmagnetic such as aluminumor some steel alloys are preferred to avoid any distortion to themagnetic field produced by the induction coils described below. In somecircumstances, the dies may be strong enough without the strongbacks.

Both the upper 20 and lower 22 dies hold inserts 46 and 48 (FIGS. 2 and5) and are reinforced with a plurality of fiberglass rods 32 (FIG. 5)that extend both longitudinally and transversely in a grid through eachdie. Each die may be attached to its strongback by any suitablefastening devices such as bolting or clamping. In the preferredembodiment, both dies are mounted on support plates 76 (FIG. 5) whichare held in place on the respective strongbacks through the use ofclamping bars 77 (FIGS. 1 and 5). The clamping bars 77 extend around theperipheral edges of the support plates 76 and are bolted to therespective strongbacks through the use of fasteners (not shown).

The dies are not susceptible to inductive heating. A composite orceramic material that has a low coefficient of thermal expansion, goodthermal shock resistance, and relatively high compression strength ispreferred such as a castable fused silica ceramic.

A plurality of induction coils 35 (FIG. 1) extend longitudinally throughthe length of the upper and lower dies. In the preferred embodiment,four separate induction coils 35 are used, however, other numbers ofinduction coils could also be used. Each induction coil 35 is formedfrom a straight tubing section 36 that extends along the length of eachdie and a flexible coil connector 38 that joins the straight tubingsections 36 in the upper die 20 to the straight tubing sections in thelower die 22. The induction coils 35 are connected to an external powersource or coil driver 50 and to source of coolant by connectors 40located at the ends of the inductive coils.

A composite panel is formed from prepreg laid-up on a contoured surfaceof a tool and is secured within the upper 20 and lower 22 dies asdescribed in detail below. The upper 24 and lower 26 strongbacks andthus upper 20 and lower 22 dies are then brought together. The compositepanel is then inductively heated to the consolidation temperature topromote resin flow and polymerization, as described in greater detailbelow.

Cavities 42 and 44 (FIG. 2), respectively, in the dies are sized to holdan upper 46 and a lower 48 tool insert. The upper tool insert 46includes a contoured forming surface 58 that has a shape correspondingto the desired shape of the outer mold line surface of the compositepart to be formed. The lower tool insert determines the inner mold line.The tool inserts generally are not susceptible to inductive heating. Inthe preferred embodiment, the tool inserts are formed of a castabledielectric phenolic or ceramic.

The tool inserts could be formed as an integral part of the dies. Theseparate die and tool insert configuration shown is preferred because itallows different tool inserts having different forming surfaces to beused in the same dies, simplifying the replacement task for changing thetooling and reducing the tooling costs.

Each die surrounds and supports the respective tool insert and holds thestraight sections 36 of the induction coils in proper position inrelationship to the tool insert. In the preferred embodiment, theinterior 70 of the dies is formed of a castable phenolic or ceramic andthe exterior sides of the toolboxes are formed from precast compositephenolic resin blocks 72. In some applications, it is preferable toreinforce the phenolic or ceramic resins with chopped fibers or nonwovenor woven reinforcing mats.

To increase the strength of the phenolics or ceramics fiberglassreinforcing rods 32 are used. The rods 32 extend both longitudinally andtransversely through the precast blocks 72 and the interior 70 and arethen post-tensioned through the use of tensioning nuts 74 after castingthe interior 70. Post-tensioning the reinforcing rods 32 maintains acompressive load on the blocks 72, interior 70 and the tool inserts tomaintain the tolerances of the upper and lower tool inserts and toprevent cracking or damage of the dies are tool inserts duringconsolidation and forming operations.

The straight tubing sections 36 of the induction coils 35 are embeddedwithin the dies, and extend parallel to the bottom surface of therespective tool inserts. The induction coils may be contained within thetool inserts.

In FIG. 2, a workpiece 60 including an organic matrix composite panel isshown already laid-up and placed between the upper 46 and lower 48 toolinserts. The detailed structure of the workpiece will be described indetail below. The workpiece 60 is heated to a forming and consolidationtemperature by energizing the coils 35.

When the workpiece 60 reaches the consolidation temperature at which thematrix flows, gas pressure is applied to the workpiece by pressuresources 52 and 54. Pressure source 52 provides a pressure to the uppersurface of the workpiece 60 through a conduit 62 that passes through theupper die 20 and upper tool insert 46, while pressure source 54 appliesa pressure to the lower surface of the workpiece 60 through a conduit 64that passes through the lower die 22 and lower tool insert 48.

In FIG. 2, the composite workpiece 60 is shown partially deformedupwardly toward the forming surface 58. The pressure applied to theworkpiece 60 is maintained until the workpiece has formed to the contourof the forming surface 58 and the matrix resin has consolidated. Thepressure sources 52 and 54 may apply an equal or a differential pressureto both the upper and lower surfaces of the workpiece 60.

Pin holes (not shown) may be formed in the upper and lower tool insertsto vent gas trapped between the workpiece 60 and the forming surface 58as the workpiece deforms. Such pin holes can be coupled to a flow meterto monitor the progress of the workpiece's deformation.

When the workpiece 60 is formed and consolidated, the induction coils 35are de-energized, and the pressure relieved. The upper 46 and lower 48tool inserts and upper 20 and lower 22 dies are separated. The compositepart is removed.

Inductive heating is accomplished by providing an alternating electricalcurrent to the induction coils 35 within which the workpiece ispositioned. This alternating current produces an alternating magneticfield in the vicinity of the inductive coils that heats the workpiecevia eddy current heating.

Curved sections 84 extending between the straight sections 36 (FIG. 4)in the coils 35 are flexible, to accommodate the opening and closing ofthe upper 20 and lower 22 dies. The curved sections 84 and straightsections 36 are joined at fittings 86 into one or more induction coilsor helixes to produce a magnetic field schematically illustrated byfield lines 90 in FIG. 3. Each straight section 36 and curved section 84preferably comprises a copper tube having an interior longitudinalpassage 96 through which a cooling fluid (such as water) may be pumpedto cool the coils during operation.

FIG. 4 illustrates a preferred construction for each curved section 84.Each curved section includes a pair of fittings 86, each of whichincludes a relatively small diameter section 92 dimensioned to fitsnugly within a straight section 36, and a larger diameter flange 94.The flange 94 regulates the distance the fittings 86 extend into thestraight sections 36. The passage 96 extends through each fitting 86,each curved section 84, and each straight section 36.

A braided flexible conductor 98 extends through passage 96 and is joinedbetween flanges 94 by a suitable method such as brazing or soldering.Finally, a flexible, insulating jacket 100 is placed around theconductor 98 and extends between the flanges 94 to contain theconductors and cooling fluid. One commercial vendor through which asuitable design cable can be obtained is Flex-Cable located at Troy,Mich.

The frequency at which the coil driver 50 (FIG. 2) drives the coils 35depends upon the nature of the workpiece 60. Current penetration ofcopper at 3 kHz. is approximately 0.06 inches, while penetration at 10kHz. is approximately 0.03 inches. The shape of the coil also has asignificant effect upon the magnetic field uniformity. Field uniformityis important because temperature uniformity in the workpiece is directlyaffected by the uniformity of the magnetic field. Uniform heatinginsures that different portions of the workpiece will reach the formingand consolidation temperature of the composite material at approximatelythe same time. Solenoidal type induction coils provide a uniformmagnetic field, and are therefore preferred. Greater field uniformity isproduced in a workpiece that is symmetric around the center line of theinduction coil. The additions of variations, such as series/parallelinduction coil combinations, variable turn spacings and distancesbetween the part and the induction coil can be established by standardelectrical calculations.

Dielectric materials for the tool inserts and dies are generallythermally insulating. Thus, the tool inserts and dies tend to trap andcontain heat within the workpiece. Since the dies and tool inserts arenot inductively heated, and act as insulators maintaining heat withinthe workpiece, the present invention requires far less energy to formand consolidate the composite panel than conventional autoclave orresistive hot press methods.

The forming operation of the present invention also takes much less timethan prior art forming operations because time is not expended elevatingthe large thermal mass of either the dies or tool inserts prior toforming and consolidating the composite panel. Only the workpiece itselfis heated by the coils. Thus, forming temperatures are achieved morerapidly and when the driver 50 is de-energized, the dies and theworkpiece cool rapidly to a temperature at which the part may beremoved, saving time and energy. In addition, the thermal cycle is notlimited by the heating and cooling cycle of the equipment and tools sothe thermocycle may be better tailored to the material used.

In FIG. 7, block 130, a composite panel 110 is laid-up from individuallayers of prepreg. The composite panel 110 is placed between a firstsheet 112 and second sheet 114 of a susceptor (block 132) to form aworkpiece. The susceptors are welded around the periphery thus forming apressure zone 117 between the susceptors surrounding the composite panel110. The resulting workpiece is then placed within the upper 46 andlower 48 tool inserts, block 136.

The periphery of the workpiece, including the area containing thesealing weld 116, is clamped between the edges of the upper 46 and lower48 tool inserts to form a pressure zone 119 between the lower toolinsert 48 and the workpiece 60 and a pressure zone 120 between the uppertool insert 46 and the workpiece 60.

In cases where the lower tool insert 48 is formed of a material that issomewhat porous, it is advantageous to place a third susceptor 122between the lower tool insert 48 and the first sheet 112 to serve as apressure barrier between the workpiece 60 and the lower tool insert 48.When a third susceptor 122 is used, it is also advantageous to weld itto the first sheet 112 around the periphery at weld 116, thus formingthe pressure zone 119 between the first sheet 112 and third sheet 122 asopposed to between the first sheet 112 and the lower tool insert 48. Inorder to ensure that the periphery of the upper and lower tool insertsare sealed it is also advantageous to use an O-ring seal 124 around theperiphery of the upper and lower tool inserts.

After placing the workpiece between the upper 46 and lower 48 toolinserts and bringing the tool inserts together to form pressure zones117, 119 and 120, the air from within the pressure zone 117 surroundingthe composite panel 110 is evacuated (block 137). Pulling a vacuumaround the composite panel 110 helps to reduce voids or in the completedcomposite pan. Pulling a vacuum in the pressure zone 117 also helps toensure that the first sheet 112 and second sheet 114 remain tightlyagainst the composite panel 110 during consolidation and forming whichin turn helps to prevent wrinkles and flaws in the surface of thecompleted part.

After pulling a vacuum in pressure zone 117, the coils 35 are energizedby the coil driver 50 with a time varying electrical field (block 138)to heat the susceptors inductively to the forming and consolidationtemperature of the composite panel 110. Heat is transferred byconduction into the composite panel 110, so it too reaches consolidationtemperature.

Pressure zone 119 is pressurized (block 140) to force the susceptors andcomposite panel 110 upwardly, as shown in sequential FIGS. 6A-C, untilthe upper surface of the workpiece conforms to the forming surface 58 ofthe upper tool insert. The pressure within the pressure zone 119 ismaintained until the composite panel 110 has fully formed andconsolidated.

During forming, it may be advantageous to pressurize the pressure zone120 between the upper tool insert 46 and the second sheet 114.Pressurizing pressure zone 120 places a force on the workpiece whichhelps to consolidate the composite panel 110 and regulates the rate atwhich the workpiece deforms. In some applications, it may beadvantageous to pressurize and maintain pressure zones 119 and 120 atthe surface pressure for a period of time to help consolidate thecomposite panel 110 prior to the forming procedure. As the formingprocedure begins, the pressure in pressure zone 120 can then bemaintained slightly lower than the pressure in pressure zone 119 or canbe decreased over time to allow the pressure in pressure zone 119 todeform the workpiece upwardly into contact with the forming surface 58.In the preferred embodiment, it has been found advantageous to form thesusceptors from aluminum or an aluminum alloy.

After completing consolidation, the induction coils 35 are shut off andthe workpiece and tool inserts are allowed to cool to a temperature atwhich the formed composite panel 110 may be removed from the toolinserts and first 112 and second 114 sheets (blocks 142-146). Althoughthere is some heat transfer between the workpiece and the tool inserts,it is insufficient to heat the tool inserts or dies substantially.

In one example of composite consolidation and forming in accordance withthe present invention, a composite panel formed of 48 layers ofthermoplastic PEEK/IM6 prepreg 3/8 inch thick was consolidated andformed. Three aluminum sheets having a thickness of 1/16 inch wereplaced around the composite panel and the resulting workpiece was placedin the tool inserts and inductively heated to a temperature of 720° F.by induction heating in five minutes time. The panel was maintained at720° F. for two minutes and then cooled for twenty minutes. Pressurezone 119 was then pressurized to approximately 250 psi while pressurezone 117 was vented to atmospheric pressure. The pressure zone 120 wasnot pressurized. The pressure in pressure zone 119 was maintained for 22minutes to consolidate and cure the composite panel. The times andpressures described above are for representative purposes only and woulddiffer depending upon the composite material used and the thickness andcomplexity of the formed part.

The present invention is applicable to all types of organic matrixcomposites that is not limited to the example discussed above. Forexample, the present invention may be used to consolidate/cure boththermal setting and thermoplastic composites including epoxies,bismaleimides and polyimides.

Another problem with prior art composite forming and consolidationprocedures has been difficulty in forming a close tolerance outer moldline while also maintaining a close tolerance inner mold line on acomposite part. In FIG. 8, the tolerances of the outer mold line surface150 of the wing skin 148 must be closely maintained to ensure that anefficient aerodynamic surface is achieved. The tolerances of the innermold line surface 152 of the wing skin must also be maintained at aclose tolerance in a buildup area 154 where the wing skin is joined to aspar 144 to ensure that the wing skin 148 and spar 144 can be joinedtogether along joining surface 156 through the use of fasteners 158without the use of shims. It is not as critical to control the innermold line surface in areas 160 where the wing skin is not attached toother structures.

Composite panel 162 is placed within three sheets 164, 166, and 168 toform a workpiece that is placed within upper and lower tool inserts 170and 173, respectively. The composite panel includes a buildup area 174having additional layers of prepreg so that the buildup area is thickerthan the surrounding composite panel. Additional layers of prepreg areused in the buildup area to reinforce the composite panel in the areawhere the spar 144 (FIG. 8) is to be attached.

Similar to the preferred embodiment, the upper tool insert 170 includesa forming surface 172 that is contoured to define the outer mold line ofthe composite panel 162 after it is formed. The lower tool insert 173includes a raised portion 180 whose upper surface 182 defines the lowersurface of the workpiece after forming. The raised portion 180 is spaceda proper distance from the buildup area 174 to maintain a closetolerance on the interior mold line surface of the composite panel 162in the buildup area 179 during forming and consolidation.

The pressure zone formed between sheets 164 and 166 is evacuated. Theinduction coils are energized to inductively heat the sheets and, thus,composite panel 162. The pressure zone 184 formed between sheets 164 and168 is then pressurized to force the workpiece upwardly into contactwith the forming surface 172 and to exert hydrostatic force on the sides186 of the buildup area 174 to help maintain the required tolerances.

To ensure that proper part tolerances are maintained in the buildup area174, it may be advantageous to weld sheets 164 and 168 together alongthe edges of the buildup area 174 along weld line 188. The weld line 188help ensure that the pressure within pressure zone 184 does not forcesheets 164 and 168 apart in the buildup area 174.

Depending upon the application, it may be advantageous to maintaindifferent pressures in pressure zone 184 at different locations on thecomposite part. Welding the first sheet 164 and third sheet 168 togetheralong a weld line defines different pressure zones between the sheetsthat may be pressurized at different pressures.

Holes are drilled in the build-up section 174 of the wing skin toreceive fasteners 158 to join the spar 144 to the wing skin (FIG. 8).

While preferred embodiments of the invention has been illustrated anddescribed, those skilled in the art will appreciate that various changescan be made therein without departing from the spirit and scope of theinvention.

We claim:
 1. A system for doing at least one of consolidating andforming organic matrix composites by inductive heating, comprising:(a)opposed dies formed of a ceramic or composite material not susceptibleto inductive heating, having a low coefficient of thermal expansion,thermal shock resistance, high compression strength, and adapted toreceive a workpiece on a forming surface; (b) an induction coil embeddedin at least one die adjacent the forming surface; (c) a workpiece seatedon the forming surface, the workpiece including a susceptor sealinglysurrounding an organic matrix composite panel to define a pressure zonearound the panel; (d) a pressure source for supplying at least about 250psi consolidation pressure to at least one side of the workpiece to formthe workpiece against the forming surface of the die when the panel isat a forming and consolidation temperature; and (e) means for energizingthe induction coil to heat the susceptor inductively and thereby to heatthe panel to the forming and consolidation temperature.
 2. The system ofclaim 1, wherein the dies include a cast material within a moldcomprising a phenolic resin box.
 3. The system of claim 1, wherein theinduction coil is embedded in both dies and includes a flexibleconnector between the dies that allows for movement of the dies inrelation to each other.
 4. The system of claim 1, further comprising avacuum pump in fluid communication with the pressure zone for evacuatingthe pressure zone.
 5. The method of claim 1 wherein the consolidationtemperature is about 720° F.
 6. The method of claim 1 wherein thepressure is at least about 250 psi.
 7. The method of claim 1 wherein thedies are cast ceramic, include an induction coil cast within theceramic, and seal around the workpiece to insulate against heat escapingfrom the workpiece when the workpiece heats inductively.
 8. A system forconsolidating an organic matrix composite panel having an exterior moldline and an interior mold line, comprising:(a) at least one sheet formedof a material susceptible to inductive heating located adjacent anorganic matrix composite panel to form a workpiece; (b) first and secondtools formed of a material not susceptible to inductive heating locatedon opposite sides of the workpiece, the first tool including a firstforming surface having a contour that defines the exterior mold line ofthe composite panel, the second tool including a second forming surfacehaving a contour that defines at least a portion of the interior moldline of the composite panel; (c) an induction coil embedded in the firstand second tools adjacent the first and second forming surfaces,respectively; (d) a pressure source for supplying a pressure to at leastone side of the workpiece to consolidate the organic matrix compositepanel and to form one side of the workpiece to the contour of the firstforming surface and to form the opposite side of the workpiece at leastpartially to the contour of the second forming surface; and (e) meansfor energizing the induction coil to heat the sheet and, thereby, toheat the organic matrix composite panel to a forming and consolidationtemperature.
 9. The system of claim 8 wherein the energizing meansprovides an alternating current to the coil at a frequency between about3-10 kHz.
 10. The system of claim 8 wherein the coil creates atime-varying, spatially uniform magnetic field surrounding the panel toprovide substantial uniform heating of and temperature uniformity in thepanel.
 11. The system of claim 8 wherein the dies are a thermallyinsulative cast ceramic to capture heat within the panel.
 12. A systemfor consolidating an organic matrix composite, comprising:(a) an organicmatrix composite panel; (b) a first sheet, a second sheet, and a thirdsheet of a material susceptible to inductive heating, the sheetsdefining a pack, the first and second sheets of the pack being locatedon opposite sides of the organic matrix composite panel and being sealedaround a periphery to define a first pressure zone enveloping theorganic matrix composite panel, and the second and third sheets beingjoined at selected locations to define a second pressure zone; (c) firstand second corresponding dies formed of a material not susceptible toinductive heating located on opposite sides of the pack, the first dieincluding a first forming surface having a contour that defines anexterior mold line of the composite panel following forming, the secondtool including a second forming surface having a contour that defines atleast a portion of an interior mold line of the composite panelfollowing forming; (d) an induction coil embedded in each of the firstand second dies; (e) a pressure source for supplying a pressure to atleast one side of the pack to consolidate the organic matrix compositepanel and to form one side of the pack to the contour of the firstforming surface and to form the opposite side of the pack at leastpartially to the contour of the second forming surface; and (f) meansfor energizing the induction coil to heat the pack and thereby, to heatthe organic matrix composite panel to a forming and consolidationtemperature.
 13. The system of claim 12, further comprising means for atleast partially evacuating the first pressure zone and pressurizing thesecond pressure zone.
 14. The system of claim 12 further comprisingmeans for evacuating the first pressure zone and wherein the pressuresource pressurizes the second pressure zone.
 15. The system of claim 14wherein the pressure source provides at least about 250 psi pressure,the coil heats the pack to at least about 720° F., and wherein the diesare cast ceramic.